1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting device with low power consumption and/or a low laser oscillation threshold value, which reduces the contact resistance of a p-type nitride semiconductor with an electrode and the loss of injected carriers due to non-radiative surface recombination, and to a thin film deposition method of the nitride semiconductor for implementing such a device.
2. Description of the Related Art
A nitride semiconductor is a compound of nitrogen with at least one of III group elements B, Al, Ga and In, and includes BN, GaN, AlGaN, InGaN, AlInGaN and the like. Recently, much research and development have been done on such nitride semiconductors as light-emitting materials in short wavelength band ranging from visible to near-ultraviolet.
Light emitting diodes using nitride semiconductor thin films can emit light from orange to ultraviolet. Such light emitting diodes are described by S. Nakamura (Solid State Communications, Vol. 102, No. 2-3, 1997, pp. 237-248).
On the other hand, semiconductor lasers using a nitride semiconductor (called “nitride semiconductor lasers” from now on) can achieve lasing at room temperature by continuous wave operation at oscillation wavelength from about 450 nm to 370 nm. Such nitride semiconductor lasers are described by I. Akasaki et al. (Jpn. J. Appl. Phys. Part 2, vol. 36, pp. 5393, 1997). In addition, nitride semiconductor lasers with mesa stripes have been formed by dry etching. Such nitride semiconductor lasers are reported by S. Nakamura et al. (Jpn. J. Appl. Phys. Part 2, vol. 35, pp. L74, 1996).
Generally, Mg is used as a dopant to implement a p-type nitride semiconductor. However, as for GaN, the most prevalently used nitride semiconductor crystal today, the activation energy of the Mg in the GaN crystal is about 200 meV, which is much greater than the thermal energy at room temperature. Accordingly, the hole concentration of only about 1017 cm−3 can be achieved. In addition, since the GaN crystal has a large band gap, there is no appropriate metallic material with a work function enabling good ohmic contact. For these reasons, the contact resistance of the p-type GaN (p-GaN) with an electrode is order-of-magnitude greater than that of the other semiconductors, which presents a problem of preventing characteristic improvement of the light emitting devices using the nitride semiconductors.
Furthermore, the nitride semiconductor lasers with the conventional structures expose the side facets of their active layers. Thus, the carriers injected from an electrode are easy to recombine nonradiatively at the side facets of the active layers. As a result, they have a problem of increasing the laser oscillation threshold value and operation power consumption.